1. Field of the Invention
The present invention relates to a vehicle control apparatus, and more particularly to a control apparatus for a vehicle which is driven using two DC separately excited motors.
2. Description of the Related Art
FIG. 2 schematically shows two-motor type three-wheelfork lift. The two-motor type three-wheel fork lift includes front wheels 1 and 2 which serve as drive wheels and one rear wheel 3 which serves as a steering wheel. The right and left front wheels 1 and 2 are coupled with first and second DC separately excited motors 6 and 7 through transmissions 4 and 5, respectively. The front wheels 1 and 2 are rotated at the same rotational frequency in the same direction, to thereby allow the vehicle to linearly travel forward or backward. Also, the rear wheel 3 is steered, and the right and left front wheels 1 and 2 are allowed to differ in the rotational frequency in accordance with a turning radius so that the vehicle can be turned. In particular, one of the front wheels which is at an inside of turning is rotated reversely with respect to the other outer front wheel, thereby being capable of reducing the turning radius.
The circuit structure of a conventional vehicle control apparatus that controls the drive of the above motors 6 and 7 for a, fork lift will be shown in FIG. 3. One end of a switch 12 is connected with a positive electrode of a battery 11, and an armature 13, an armature current detector 14 and an armature chopper element 15 for the first motor 6 are connected in series between the other end of the switch 12 and a negative electrode of the battery 11. A flywheel diode 16 is connected in parallel to the series circuit consisting of the armature 13 and the armature current detector 14. Also, a field current control circuit section 17 for the first motor 6 is connected between the other end of the switch 12 and the negative electrode of the battery 11. The field current control circuit section 17 is designed such that a series circuit consisting of first and second field chopper elements 18 and 19 and a series circuit consisting of third and fourth field chopper elements 20 and 21 are connected in parallel to each other. A field winding 22 and a field current detector 23 for the first motor 6 are connected in series between a node A of the first and second field chopper elements 18 and 19 and a node B of the third and fourth field chopper elements 20 and 21.
Similarly, an armature 24, an armature current detector 25 and an armature chopper element 26 for the second motor 7 are connected in series between the other end of the switch 12 and the negative electrode of the battery 11. A flywheel diode 27 is connected in parallel to the series circuit consisting of the armature 24 and the armature current detector 25. Also, a field current control circuit section 28 for the second motor 7 is connected between the other end of the switch 12 and the negative electrode of the battery 11. The field current control circuit section 28 is designed such that a series circuit consisting of first and second field chopper elements 29 and 30 and a series circuit consisting of third and fourth field chopper elements 31 and 32 are connected in parallel to each other. A field winding 33 and a field current detector 34 for the second motor 7 are connected in series between a node C of the first and second field chopper elements 29 and 30 and a node D of the third and fourth field chopper elements 31 and 32.
The respective gate terminals of the armature chopper element 15 and the first to fourth field chopper elements 18 to 21 of the field current control circuit section 17 for the first motor 6, and the armature chopper element 26 and the first to fourth field chopper elements 29 to 32 of the field current control circuit section 28 for the second motor 7 are connected to a drive circuit 35, respectively. The drive circuit 35 controls the armature current and the field current for the first motor 6 by turning on/off the armature chopper element 15 and the first to fourth field chopper elements 18 to 21, and also controls the armature current and the field current for the second motor 7 by turning on/off the armature chopper element 26 and the first to fourth field chopper elements 29 to 32.
However, as is apparent from FIG. 3, because the conventional vehicle control apparatus has a circuit structure in which a control circuit for controlling the drive of the first motor 6 and a control circuit for controlling the drive of the second motor 7 are connected in parallel to each other, there arises such a problem that the number of elements that constitutes the control apparatus, in particular, the number of elements for controlling a large current are large, and the entire vehicle control apparatus increases in size.